I was wearing one helmet and could not hear my buddy speaking but they could hear me. So I started to check the connections on the bad helmet. As soon as I checked the main connection from the helmet to the SMH5, as soon as my hand touched it the noise began. I wiggled the connection and could make the loud noises at will. So at least for me it's that connection that gets wind pressure and will make a bad static. 

I also find that turning the volume down to as low as possible helps with extra static.

Still running the SMH5 after a few more battery swaps. I got a few off of eBay that worked but I had to solder on the wires together as the little plugs are just too damn hard to plug in with the new battery.

The one I have is marked 6SP652535 400mAH 1.48Wh. Make sure the battery size is not larger than the one you take out.

I've gotten now 5 years out of the SMH5 and have purchased a few used from eBay so I'll be using them for a long time to come. I've gone through 3 motorcycles and 3 batteries in this time..