My variation on "cracking sound" problem

I'm running Sonar X3 Producer. I have a Windows 7 32bit system. I have two USB audio interfaces: an M-Audio Fast Track and a Tascam US-800.
I'm getting bad "crackling" in the audio with both of them, with the following particulars (I don't usually keep both of the audio interfaces in the system at the same time; for this testing I was using one and then the other).
(1)If I record into Sonar thru the M-Audio, I get bad crackling during record and playback. The crackling is also there when I EXPORT the audio file.
(2)If I record into Sonar thru the US-800, I get bad crackling during record and playback. However, the crackling is NOT present in the exported audio file. ALSO, the crackling is not there in Sonar playback if I change the playback device to ASIO and my computer's default soundcard. Plays back thru the computer speakers nice and clean.
(3)For comparison, I recorded into SONY SOUNDFORGE through the US-800. Bad crackling during recording, and bad crackling during playback if I play back through the US-800. If I change the playback audio to either Windows Sound Mapper or Windows Classic Wave Driver, there is NO crackling in the recorded audio. There is also NO crackling if I Save ("export", in Sonar's terminology) the recorded file to mp3 or wav and play that.
MY CONCLUSION SO FAR is that I'm having a problem with my computer's USB handling. (I tried a built-in front USB2 port and a plugin-card-based USB3 port, and a slot in an external USB hub. Same results in all cases.)
I've also tried rebooting my system. No help.
 
I sure can't think of anything else to do.
I've Googled extensively re USB problems in Windows7, but no proposed "solution" does any good.
If absolutely necessary, I can live with hearing nasty crackling while I'm recording (even during overdubbing/multitracking), but life would sure be much nicer if that weren't happening.
 

This seems to most likely be settings issues, so once you post your system details, as well as the other stuff I list below, we can likely help get you fixed up:
 
Audio Interface: Sample Rate and ASIO Buffer Size
 
Sonar: Sample Rate, Record Bit-Depth, Driver Mode, reported Total Roundtrip Latency
 
I would recommend the following settings, by the way, to start with:
 
Audio interface: Sample Rate of either 44.1 k or 48 k, and an ASIO Buffer Size of 128
 
Sonar: Sample rate must match the sample rate your audio interface is set to, also Driver Mode of ASIO, record Bit-Depth of 24 bits, and try to get your total roundtrip latency down to about 10 milliseconds or just a little bit under that.
 
And, pick one interface or the other, for the moment, with the above settings, and post back how that sounds, along with the reported total rountrip latency.
 
In addition, just for purposes of the testing of the above, please record with no plugins, so that we are just dealing with the settings and not any additional variables from any plugins.
 
Thanks, 
 
Bob Bone