I have a 2013 XC70, T6 engine, 137,000 miles, always kept up to date with maintenance/oil changes/etc, no codes I'm aware of. It has a rattle upon acceleration which only appears when the engine is fully warmed up.

Rattle is most noticeable at speeds between 20-30mph and especially on an incline. The rattle is only audible with windows down and also when there are cars parked on the side of the road or other hard objects that reflect the sound back, so I'm guessing it is related to something on the bottom of the car?? One other strange thing is that it's much more audible in the summer months when weather is hot, in winter the rattle is very rare (I've tried driving with windows down in winter to listen for it).

The rattle has been there for more than three years and I've been unable to fix it, so any advice is appreciated!

I've always kept up to date with all maintenance with the dealer and other reputable independent repair shops, but nobody is able to fix the rattle. I just got the car back from the shop where they checked the whole car over and saw the exhaust was loose so they replaced exhaust hangers but the sound is still there. I've gone under the car to find any loose components but I am not able to find any (although I'm not very knowledgable with cars).

Can you please suggest anywhere else I should look?