I recently bought a 2" 24 track 3M M79 and I'm having some issues with static-like popping sounds coming from the repro head on playback. Sometimes it won't do it for several minutes but sometimes it does it more often.

I had the repro head re-lapped by JRF and I'm wondering if it's related... i there something I could have done wrong in mounting the head assembly that could be causing this?

Does it happen when your monitoring off the sync head, repro, or both?
There are numerous possibilities. Sometimes static electricity stores on the tape backing, then discharges on the playback heads (being the first, best ground available).
Call J. French for some advice first, but there are ways to half-ass discharge the tape before it reaches the heads.
Sit and listen to the machine, stopped, in repro, to see if noise occurs.
Check to see if it happens while playing another tape (preferably, another formulation, or year).
Report back if you find a solution, I'm interested.

Thanks for the advice.

It only happens on the repro head when the machine is playing.

I'm gonna talk to J. French and I'll let you know if I get it figured out.