New variable in the bubbling/gurgling/croaking engine

It seems it's no longer consistant. Yesterday I was accelerating up the freeway and the engine was quiet as new, no noises whatsoever. Just to make sure it wasn't a fluke, at the next stop sign I ran into I floored it with the radio off. No noises. Later at night when I started her up sure enough it was there again, but the noise grew softer after my engine had warmed up all the way. Anyone beginning to think this is oil related? My dealership insists that it's an easily fixable valve lift problem (and ever time I go in they twist something under the hood and voila -- fixed for 15 minutes). It's left me flat out stumped.