C-15 squealing

One of my C-15's has developed a squealing noise under power and jakeing. It's an MXS ACERT. The sound resembles a squealing belt or the sound when you slowly let the air out of a balloon. It is coming from the pass side and appears to be turbo related. I checked all hump hoses for leaks, pressure tested the CAC and checked both turbos. Both have smooth free bearings and neither are rubbing the housing. I also checked the waste gate and it appears to be closing all the way. I checked all of the bellows and all appear intact with no cracks. I don't see any evidence of an exhaust leak anywhere. As near as I can tell there are no leaks on either the suction or pressure side of the turbos although I may be missing somewhere to look. On power, rather than a nice clean turbo whistle, it squeals, on Jakeing, the squealing is the same but flutters slightly. I'm obviously missing something. Thoughts?.

 

Did that, soapy water on all pressure connections also sprayed a bit of ether around suction side connections as well as on the steel bellows (looking for cracks). No sign of leaks.