- DAS
Assuming it is in the cabinet it almost has to be one of two things:
1) Something is lose - could be a screw, the surround of a speaker, the grill, a handle, a wood joint, etc. These can be really hard to track down sometimes. Sometimes they just go away....
2) A speaker is failing. Occasionally the voice coil of the speaker will slightly rub inside of the magnet gap. In more severe cases this will sound like radio static, but sometimes it can have a character like what you describe. Causes can be numerous, but the fix is a speaker re-cone or replacement. The one exception could be that sometimes if a cabinet gets banged hard in the right way the wood of the baffle can become stressed, which can put some torque on a speaker and cause some of the rubbing. That's pretty rare though.
Unfortunately you may just have to wait to see if it gets worse before you spend much more time chasing it down.
I am currently running a Hartke 4.5 XL cabinet with a Hartke 3500A amp. Recently, my cabinet has began making a weird noise off and on when I play the low E string. It's not a hissing but more of a paper blowing in the wind sound. At first I thought it was a blown speaker, but it only does it every now and then, and only when I play on the low E. I've taken it to shops but of course, it worked fine at the time and they could offer no help
Has anyone heard of this before? Thanks for the help.