Ford Connect 110 rattle

[Heaveho]

I've got a 59 plate Connect 110 with 47k miles, FSH, and it also gets the oil and filter changed every 5k miles. In the last couple of days it's developed a rattle at about the same revs as when it comes on boost, most easily replicated when in 3rd gear, feathering on and off the throttle at about 1800 rpm. I've heard it in lower gears and possibly 4th, but the van generally starts to get noisier then anyway, so hard to tell in the higher gears. It won't do it when revved in neutral, and the noise disappears immediately when not under load. It drives, comes on boost and changes gear absolutely as normal, and if I couldn't hear the noise I wouldn't know anything was amiss.

I've had the inlet pipe off and there's no play on the turbo shaft. It's a variable nozzle type on these if it makes any difference. I've been around the underneath with a rubber mallet and there's nothing that can be made to replicate the rattle, including the cat.

I'm wondering about the DMF, but I've only heard these rattle at tickover. Mine's quiet at tickover. I can't be sure yet, but it seems worse on corners, maybe imagining that though. Can a DMF that's on the way out just rattle randomly at any revs?

Any input appreciated, I'm nervous that if it's the turbo, it lets go and takes the engine with it.