DJM900 from the US - Sound Quality Problems

I'm currently using a DJM900 from the US in the UK. I have a step down transformer for it which has worked well for a number of months now, however over the past few weeks I've experienced some sound quality issues - what sounds like very distant/muffled lows (similar to bad clipping) when recording and playing through speakers. I've tried a number of different things - including checking all settings are as they should be, I'm not redlighting, I've changed the USB cable that connects the DJM to my laptop, updated the drivers and hardware, tested to make sure I haven't created an electrical ground loop, connected the mixer to a different laptop to ensure its not a problem with my laptop, among other things, which has all led me to believe it is in fact the DJM and/or the transformer that's not working. I'm going to replace the transformer to see if this makes a difference but was wondering if anyone has come across a similar issue before or has any thoughts/suggestions.

Thanks,
Katie