If you've recently replaced the belt as well then i don't know. But in my case I have the occasional squeak and my theory is that at least part of the problem is an old and stiff belt.
The squeak is much worse at start up especially winter time and often stops when the engine has warmed up, now in the summer it seems to be fairly silent. When the belt is stiff it simply will take longer to smooth out the the form it has got when remaining stopped. This also means that an old belt will put more strain on the tensioner as well while the "bumpy" stiff belt rotates.
The squeak is much worse at start up especially winter time and often stops when the engine has warmed up, now in the summer it seems to be fairly silent. When the belt is stiff it simply will take longer to smooth out the the form it has got when remaining stopped. This also means that an old belt will put more strain on the tensioner as well while the "bumpy" stiff belt rotates.