Ls1unearthed

Hey guys,
I have been a member about 2 yrs and this is my 1st post, that said....

I NEED HELP...

I have a mostly stock 2000 Z,and about a month ago I had her trans rebuilt.
She ran about a week but when it rained I went out to start her and as soon as I turned the key to accessory she started but with a god awful noise like the starter wont disengage,i shift to drive or reverse and the noise stops but as soon as I try to put her in park the sound starts again.when in drive or reverse she runs like a champ, I don't get it, Could this be as simple as a messed up starter or a gateway to a much bigger problem?? oh yeah, it only happens when it rains. never had it happen on a nice day...
thanks guys,
Derek.