When I turn on my amp, I noticed little hissing and crackling sounds. I understand that every amp will produce some noise, but the noise should be constant. I noticed however, that the hiss seems louder than usual and there are also some minor crackling sounds that are very irritating. I have a Hartke 3500 head and 410 speakers. The head seems to be sensitive to touch because when I touch the knobs or mess with the input jack, the crackling gets worse. Also, when I change the EQ, the EQ of the hiss changes. (I guess that's natural though.) What could be the problem? Is this occurring perhaps due to dust? Thanks.