2013 Thunderbird problem

[Spike66]

I'm not a bass player but guitar and mandolin but I wanted a bass and bought a 2013 Thunderbird on Saturday. It played great but the strings looked like they were original since the guy said it had been in the case most of its life under a bed. I got some new strings (Slinky Cobalt) and I wanted to give a good cleaning. I didn't realize the bridge wasn't fixed to the body so when I took the last string off and tipped the guitar it fell off. No big deal I cleaned it and put the new strings on and tuned it up. When I plugged it back in it has a horrible electronic buzz that it didn't have pre changing of the strings.  By horrible I mean I can no longer record a bass track without hearing the buzz in the track.  Before the restring I could record and no buzz just bass. All I did was changed the strings and put the bridge back on. Possible grounding issue when the bridge fell off? I searched the internet to see if there was suppose to be some type of grounding wire to the bridge but found nothing( I know nothing of electronics but I'm willing to learn it now). I just put it back in its case because I don't want to play it until I find out whats going on and fix it. Any ideas of what I might have done and any tips to trouble shoot and fix the issue? thanks