Erratic chirping noise from engine bay

[Jmwilkins63]

2008 Mark 5 DSG gti with 44k, had timing belt and water pump changed 2021. Erratic chirping noise( sounds a bit like belts slipping but had checked and all fine). Happens whilst driving along at c 1500 revs, not accelerating, very intermittent, not at time of gear change, more pronounced when engine warm.  The car idles well, no error codes. Checked PCV and all looks good( cannot take off engine filler cap whilst engine running, thought might be aircon but noise still when turned off.  A mechanic thought maybe Turbo intake but happens when turbo not kicking in. Does anyone have any ideas?

[LC5F]

Alternator pulley has a slip mechanism or AC pully - diagnose by slackening the tensioner on the drive belt

[Jmwilkins63]

Thanks, will try this, the noise though does appear to be from the rear of the bay