wondom jab5 4x100w hiss noise

Hi....I am using a wondom jab5 4x100w for my two way 6"woofer + 1" tweeter project and am noticing a strange problem. When going all 4 channels I am getting a lot of hiss noise from amp. If I use a passive crossover and use 2x200w mode the noise is completely gone. Anyone have an idea what is going on?

Tnx,
Milos