DI doing different things through different PAs

[ThomBassmonkey]

After playing my MB Fusion at various venues and being DId by various PAs, I'm starting to notice that it doesn't seem to agree with some PAs.

Before playing, I fix my on-stage volumes (I'm pretty good at judging the right volume for the gig, I rarely get asked to turn up/down by engineers), sort both gain structures (going to call them channels from now on, even though technically they're not) so I have one clean and one overdriven so they're even and if needed I EQ a little. As far as I can remember, I think I've only been asked to change volume once recently without me being unsure and asking the engineer myself (even then 9/10 times I'm fine).

Once it's gone through the PA though, one of several things happens.

1. Everything's fine. My two gain structures come out even and there's no buzz. This is the majority of gigs, the problems have only happened maybe once or twice each.
2. The OD channel is much louder than the clean. I can fix this on my head by turning down the OD level, but then when I'm using that it's much quieter than the clean through my cabs, not caused a problem yet as it's only happened at gigs where I'm just DI'd, if I was micd too though it could be an issue. This has only happened once or twice.
3. There's buzz on the OD channel, only happened once and it was very quiet (didn't cause any problems at the gig, though it was audible when we weren't playing if I left my amp on the OD channel though not enough that it would've been annoying but it was only a small-ish gig).
4. There's buzz on both channels, only happened the once but it was annoying as I ended up with the DI before my amp so no distortion coming through the DI, though I was micd too so there would've been some distortion out front. It was at a festival and the engineer didn't seem very inclined to let me try out alternatives (which is understandable on the main stage when there's god knows how many bands) so I didn't get to try out the ground switch or putting the DI in the FX loop.

All of the problems could be explained (I think) by either grounding issues or gain problems with the desk, but they're not problems that I've heard about or have had before with my other GK rig (though I've not used this rig at venues I've played with my other rig so it could've happened with both). I assume the DI is going to be very similar on both since they're both the top of the range amps by the same company, so I'm wondering if there's a fault. I'm going to be asking GK about it too but since it's the weekend, there's no harm to be done by asking here.

The only DI related controls are pre/post EQ and a ground switch. There's no DI specific output knob.

Thanks!