what you were probably hearing were Carp or Buffalo rolling/feeding (did you hear any "sucking sounds" ??). They will come to the surface and roll in the debris - sucking in the "trash" floating on top. It's pretty safe to say that, if it was Carp or Buffalo, there were probably not any Crappie around.
Receding water generally pulls Crappie out away from the bank, and they suspend or head for deep cover. Cold & muddy water is the worst condition you can face, this time of year. Yo-yoing water levels only add to the negative side of things. Even warm & muddy water, that isn't stable, isn't all that good. A slowly rising or falling water level, even in flooded conditions, will afford you a chance at catching "some" Crappie ... I did it at Barkley Lake (many years back) by getting up amongst the "live" trees that were flooded (with 2-5ft of water up the trunks). I used a spinning outfit / minnow & float rig / 1.5ft depth (from float to minnow) ... I placed the minnow along side every good sized tree I could get to - right beside the tree and on all four "sides" of each tree. Seems the Crappie were nosed right up against the live trees, on the flooded banks (waiting for the water to stabilize ??). I don't know if they would do the same on your lake ... but, if you go, it may be worth a try (under similar conditions).
I've also heard that Crappie like to hide, real shallow, up under those floating mats of sticks & debris. Makes sense - they've got overhead cover, warmer surface water, and they'd be in the water that clears up first (upper surface level). Finding the clearer waters, like in the back of creeks & bays & pockets, is also an option ... esp. if the rains continue and they're warm rains (and not heavy downpours) - this will send clearer water from the incoming creeks, into the backs of these areas, and the fish should migrate towards that incoming warm water.
I know how you feel, brother ... my local Crappie lake was just starting to produce some catches, then we got some locally heavy rains - now the lake is 9ft above Summer Pool !! That effectively shuts down that lake for a week or more ... until it settles out, and if no more heavy rains occur. I haven't wet a line all year, and the Spring Fling tourney is slipping up on me, quick ! Between the weather and my changing work schedule ... looks like I may have to go into the tourney - cold turkey...luck2ya ...cp