Open Astro XTS3000 CPS and expand on the RADIO CONFIGURATION menu and click on the RADIO WIDE menu pull down list then look for AUDIO GAIN OPTIONS and see if ANALOG is checked. If so uncheck it, this may or may not be your problem.
If it is not checked then I'd suspect that your radios RF board may have been changed out and not properly aligned and this sounds more like your problem.
The repeaters IF bandwidth is probably tighter than the IF bandwidth of the radio that you are using to listen to in talkaround mode.
Or the repeater could also be passing thru CTCSS tones which if they are excessively high will cause distortion on the repeated audio.
You will need to use ASTRO RADIO Tuner and go into the TRANSMITTER ALIGNMENTS and look for TRANSMITTER DEVIATION LIMIT, you will need to click on help the see the correct alignment procedure.
Another thing which may cause the problem is the TX DEVIATION BALANCE being misaligned, this is also is in the same Astro TUNER TX alignment menu.
If the low frequency compensation is set to high then CTCSS tone deviation will be excessive causing audible hum in the TX as mentioned above.
The excessive CTCSS Deviation may come across higher than normal when transmitting thru the repeater, especially if the repeater is not balanced correctly between RX and TX.
While in Tuner also check the REFERENCE OSCILLATOR and make sure it is set on frequency.
Either way if you go into TUNER you will need some way to measure CTCSS tone and TX audio deviation along with the tx frequency.
Mike