I'm not overly familiar with that engine in particular but I'd be surprised if it has a recirculating valve at all (or atmospheric dump valve, which certainly wouldn't be OEM).
Many diesels simply don't have throttle body – or at least not one that's used in a conventional fashion, and it might just be dubbed a flap or valve – so there's no need to recirculate or dump the pressurised charge in the intake, because it can always enter the engine.
I must admit that I'm not sure about modern diesels with throttle-style assemblies designed to aid with emissions controls or runaway conditions, among other things, but I'd imagine a recirculating valve is probably uncalled for there, too. For the most part, the only reason most petrol-engined turbocharged cars have them is due to noise reasons – and perhaps a handful of longevity-related considerations, IMO.
The reason you're hearing it prominently is because of your cone filter. The factory airbox would muffle most of that noise, if not all. In your clips, I think the engine is actually under slightly more load and building a bit more boost in the first, hence it being prominent. At the very end of your second clip, there is a momentary chatter. It'll vary with engine, load and ambient conditions, as an aside, so it'll sometimes do it, sometimes not.
And, after a quick search, that TDCI does appear to have a throttle body of sorts, which presumably is used for EGR-related functions – so it might be that you're hearing it in the instances that the blade is partially closed to aid EGR flow, which would trap a bit of pressure in the intake, exacerbating that chatter. Might explain why it comes and goes.
That might not be the case, of course, but did just cross my mind after I actually thought about it for a moment... No doubt someone more informed will be able to fill us in on the details, as it's not something I'd ever really considered.
I wouldn't worry too much about it, provided it's otherwise driving fine and not showing any signs of distress. Put the factory airbox back on and see what it does, if you're curious.
