Check your audio cables - make sure no shorts anywhere (an EBTECH Swizz Army© tester is great for this), and of course, make sure your speakers are in phase. Then be sure you are not creating a low level feedback loop somewhere in your routing scheme (might explain the pinging). If some of your keyboards/modules have digital outs and you are using them, make sure the sample rate is the same as what your system is recording at. One time I plugged the digital out of a Kurzweil into a system recording at 44.1, not realizing the Kurzweil only outputted 48k. You never heard such a god-awful sound! If all that checks out, maybe it's just a gain-staging issue. It only takes one link in the audio chain (synth output/preamp/compressor/DAW input/software plug-in/aux send/digital or analog fx/etc.) driven to clipping to destroy the whole sound. Try eliminating as much as possible in the chain, then adding stuff back in one by one to isolate the problem. Start by playing your synth into a simple keyboard amp, and go from there. Also check for mismatches: maybe you have some pro (+4) level outputs driving "consumer" (-10) inputs. Good luck.

Littledog has some good suggestions... if none of that changes anything, you might need to do some acoustic treatment on your room. Give us a description of the room and its measurements, maybe something will stick out.

This could be any zillion number of things. Are you familar with your monitors? Do CD's sound just as harsh, etc when you play them in your system? Does your setup sound bad before recording? If you're in a rush, try talking a store clerk into droppin' by & troubleshooting. If you bought a lot of stuff, they are usually pretty forthcoming.