Noise, Toyota Paseo, Even when belts are new !

1997 Toyota Paseo ( Non-convertible)
Mileage: 108,400

Initially when I used to start the car there used to be this screeching noise. :Cry:
. When I replaced them, now at least when I start the car there is no problem. But now it screeches when I accelerate but then goes away. But in the morning when the engine is cold, there is absolutely no screeching noise. Why is this happening? Again yesterday when 4 friends were sitting in the car it gave a terrible Loud noise. Is it because the car is taking more weight? ( I had brakes worn off and I replaced them, New brake pad and New Rotor, since I had some problem with brakes too )

I am really concerned since I am spending money like anything and the problems just keep on cropping.

Any advice will be extremely helpful,

Thanks.