I had this exact 'elephant' 'trumpeting' noise yesterday in our D5 XC90 and only when under load and the turbo spooling up. Sounded like the gushing turbo air sound was excessive also.
I found this post and it appears the original person never posted the fix.
I had a look at the resonator and pipe assembly under the turbo beneath the engine/transmission. I could see at the turbo outlet the resonator had slipped down maybe 10mm and a clean section of the orange rubber connector sleeve was visible. I began to think whether there was a split in it and the turbo pressure was creating the trumpeting noise. A bit like a reed in an air instrument. I also noticed one of the mounting points on the pipe had split (I recently replaced all engine mounts, had to source the parts from autodoc in the UK as nothing available in Oz - I guess the busted mounts caused excessive vibration over time and the pipe mount split then)
I removed the resonator and bingo the top orange seal/connector was split. Bought new ones from Volvo for $30, cleaned parts and refitted. Cable tied the pipe through the existing mount hole. The new seals made it a crazy tight fit which required a smear of synthetic assembly lube similar to Vaseline but not a solvent oil base so is safe on standard rubber and some pushing, levering and persistence to sit snug against the turbo and pipe sections.
Car is running great again!!!
I know this is a very old post however wanted to share should someone in the future have this issue which I now understand is a common failure.
Cheers and beers people
Ryan
