I reworked this a bit and it may have fixed it. Requires more testing due to how inconsistent this problem is in Firefox. We shall see!

Nope. Not solved yet. This problem sucks.

I think this problem has been greatly reduced now.

the problem i am having is i play with all sounds to set to 0, now i am hearing sounds regardless of the settings. Had to mute my tv in order not to hear sounds

That is a new bug I added.

The sound today has been much more reliable. Not sure if that has anything to do with the flash player update i did this morning but i haven't had the hissing and popping problem. And i've kept sound longer, though i haven't played my higher level chars yet today so not sure if combat will kill it.

Will fix the audio volume today. Was testing and forgot to take the volume line out.

OMG! I am 99% sure I just fixed this!!!!! I discovered that if you try to play a blank audio file it will sometimes make this noise. Basically some mobs have empty noise slots assigned to them because some mobs don't make casting noises or idle noises, so it would end up making that drill noise sometimes. I noticed it would do it often when clicking Search Battle, so I checked that specific function to see if I could figure it out. I checked the sound effect it was trying to play and I found it! HA! I am so happy!

So far so good.

Got the dreaded hisspop in Halas just now.

I had the same problem in Kelethin last night. Or at least I am 90% sure it was Kelethin.

Thanks for reporting. The good news it's an easy fix. I just have to put a return in the music function, too. I forgot I sent it empty audio sometimes. Thanks a ton guys!