Trouble has a habit of providing an overture to the release of Wilco albums. In 2002, you’ll recall, Wilco’s former label Reprise rejected Yankee Hotel Foxtrot as too uncommercial and sold the masters to the band for $50,000, who then streamed them on their website, signed a new deal with Nonesuch (like Reprise, a Warners subsidiary) and found themselves in the US Top 20. Once perceived as the quintessential alt.country act, Jeff Tweedy and Wilco emerged from the fracas as rueful, empowered popularisers of the avant-garde, after a fashion.

This time, A Ghost Is Born, Wilco’s fifth album, has been briefly delayed thanks to Tweedy putting himself into rehab to treat an addiction to painkillers. For years, it’s transpired, he has been poleaxed by migraine headaches, and their effects reportedly disrupted the recording sessions for A Ghost Is Born. His dependency, official channels suggest, stems from attempts to control this debilitating condition.

It’s tempting to scour the album for evidence of Tweedy’s problems. As ever, his lyrics are more allusive than direct, and the resigned timbre of his voice continues to evoke despondency when the words suggest something quite different. “I’ve been puking,” he notes during “Company In My Back”, while “Wishful Thinking” asks, “Is any song worth singing if it doesn’t help?” Can the music of Wilco?rich, inventive, diverse, volatile?be a palliative to Tweedy’s pain? Is his increasing love of drone, which culminates in the vast minimalist hum of “Less Than You Think”, a way of musically transcribing the engulfing presence of a headache?

These are questions that, currently, remain the business of Tweedy and his doctors. In the meantime, a gentler study of this marvellous record initially suggests it’s a lot more easy-going than Yankee Hotel Foxtrot. The backdrop of static and laptop interference that made YHF at once warm and alien has gone?though that album’s inspired mixer, Jim O’Rourke, has been promoted to co-producer. The electronic texturing to A Ghost Is Born is comparatively discreet, leaving the band more space to manoeuvre. It’s an organic, intuitive record on which Wilco sound wonderfully free of constraints.

Part of this is down to the absence of Jay Bennett, Tweedy’s co-songwriter, who left acrimoniously towards the end of the recording of YHF. The departure of the relatively conservative Bennett, you’d imagine, would allow Tweedy to navigate a course further into leftfield American music. It’s a surprise, then, to discover that Wilco’s first post-Bennett album begins in straightforward fashion. “At Least That’s What You Said” is a pensive ballad in which Tweedy and pianist Mikael Jorgensen quietly circle each other. After two minutes, however, Tweedy launches into an exhilarating guitar solo. For a minute or two, it broadly follows the Neil Young template?weighty, sloppy, lashed with feedback. But as it progresses, Tweedy starts taking more risks, unleashing pointillist skrees of noise, recreating the radio friction of YHF by manually attacking his guitar. It’s thrilling to hear and sounds enormously liberating, too.

“I felt a lot freer,” Tweedy said before he entered rehab. “I was actually inhibited about my playing for many years, so I think there was some effort to let it all hang out.” The results are spectacular. A Ghost Is Born takes a fairly orthodox rock set-up and applies a new expressive flourish. “I’m A Wheel” might revisit the Stones fetish Tweedy showed on 1996’s Being There, but the jutting riffs are oddly punctuated, diverting the song’s energies into cunning new directions.

The guitar heroics reach their peak early, on the third track; “Spiders (Kidsmoke)”, the best thing Tweedy has ever done. Jorgensen, bassist John Stirratt and drummer Glenn Kotche establish a pulsing motorik rhythm clearly derived from Neu!, only for Tweedy to assail it with increasingly deranged guitar solos. Again and again he sprays notes everywhere, as reminiscent of Yo La Tengo’s Ira Kaplan and free jazz guitarist Sonny Sharrock as Neil Young, before reconfiguring them into an exultant refrain. This goes on, fearlessly, for over 10 minutes.

It’s not, though, the longest song on A Ghost Is Born. That honour lies with “Less Than You Think”, another sketchy ballad that dissolves into a 15-minute harmonious drone (inspired, Stirratt confirms, by minimalist composer Terry Riley). More than ever, Wilco are disdainful here of a conventional canon to draw from. In the world of A Ghost Is Born, Sharrock and Riley are just as accessible as The Band: Jorgensen, originally recruited as an electronic manipulator, favours an ambling, soulful piano technique that’s hugely informed by Richard Manuel.

Increasingly, too, Tweedy has a knack of allying his sonic innovations to his lyrical concerns. So, on YHF, the theme was communication breakdown, whether it be garbled, encoded radio signals used as texturing, or lyrics which described long-distance misunderstandings. On A Ghost Is Born, he remains a great writer of songs (“Muzzle Of Bees”, especially) which portray love as fundamentally constant, but assailed by ambiguities, very human glitches. And in common with the album’s questing, untethered sound, Tweedy continually sings of escape and liberation. Or, at least, of an invigorating struggle to be free. You could ascribe this to the departure from Reprise or Bennett’s absence, but more likely it’s a general relief that success has excused Wilco the pressure to compromise. “It’s good to be alone!” he exclaims on “Spiders (Kidsmoke)”, and it’s tough to resist his enthusiasm for this passionate, unmediated, adventurous but always profoundly human music.

By the end, in the ramshackle singalong of “The Late Greats”, Tweedy claims, “The best songs will never get sung/The best life never leaves your lungs.” The finest music, he implies, is that which comes and goes in an instant, that is so elusive and impulsive it can never be properly captured. For A Ghost Is Born feels like a band learning to be spontaneous and unencumbered, and coming up with their most engaging album yet. The best songs might never be quite voiced but, on this form, Wilco are getting closer and closer to their essence.