I have an overflow box, but similar problem.
I fixed my noisy drain with one of those bendy-straws - bent it over as far as it would go, then inserted the long end down into the drain of the overflow. The gurgling starts up once in awhile, but it usually stops within seconds.
180G build thread
180G All-glass with dual megaflows in a custom stand
AquaC EV-180 skimmer
250 pounds LR
160 pounds aragonite
Custom acrylic sump from GlassCages.com
2xPCX-40 return pumps
2x250MH 14K, 2x175MH 14K - PFO lighting, 2x65W PC
No-name 36W UV
Water General 125GPH RO/DI