Problem with new tires in second gear only, no problem when I switch to winter tires

[Sonett43]

Ive gt a 2006 x5 4.4 sport, 17" non staggered snows and 19" staggered brand new conti extreme contact dws. 255/50-19 and 275/45-19.

These tires are 1 week old and the excelled shop, euro tire in NJ tells me they will take them back within 30 days if the trouble persists and I want other tires...

The problem ONLY happens in second gear, first is great, then in second under light or medium throttle , don't know about heavy, you just can't feel it.....there is a massive rhythmic clunk, you can almost picture it as one revelation of a wheel, or the driveshaft, clunk, clunk, clunk....then it shifts to Third gear and the problem goes away.....

Really, only in second gear, but under a variety of throttle inputs.....much like a flat spot but again, only in second gear.

Anyone experience anything like this.....I've been so impressed with the tires otherwise.....please help.