Just for record in case someone searches for belt squealing or tensioner, I have had the exact same issue as above fixed previously and it is spot on. The noise is a continuous noise that comes from the belt area, and will be going if the car is hot, cold, air con on or off. The only thing that seems to affect it, is that at speed it isnt quite as loud but is very loud at idle. The noise sounds exactly like a loose or squealing belt, because thats what it is (not getting enough tension). Mine was replaced at 90k. Unfortunately for me, my mechanic had never heard of it and speaking with Toyota they didnt seem to think that many had been done. I went through a bit of trial-and-error to fix it, which resulted in me getting the bearings on all the pulleys changed and a new belt (all cheap fixes) before I had the belt tensioner replaced. Luckily that fixed it though. The problem that the OP has though sounds much more severe.