Got to give a big shoutout to Neil Haddow and the team at Porsche East London.
My 991 started making a horrible knocking noise over speedbumps so I had a feeling something in the suspension might be playing silly buggers. Booked it in to Porsche and took the tech on a road test, he thought it might be stones in the ARB so said he'd take a look and let me know whilst I was there. No such luck with them there, but he said my undertray is filled with stones and mud so he's not ruling out that as the issue just yet, but that I would need to leave my car with them for a couple of days (this was a Saturday). No bother, left it with them with the aim to collect at the next weekend, but get a phonecall on Monday to say that they've cleaned out all the stones and the noise has gone, which is a result and I'm welcome to collect that night. Told him I had forgotten to mention it, but my electric window controls had also gone a bit funny (no one-touch, can't control the passenger window from the drivers controls but works fine from the key), Neil said leave it with him and he'll take a look.
Phoned back the next day, electric windows all fixed, and another test drive done to confirm that the knocking noise is definitely gone. Asked what my bill was and was told "we spent around an hour on the job but being honest sir, I don't have the cheek to charge you to clean out your undertray. Consider this one on us". Dropped by after work to collect it, had a quick chat with Neil and then jumped in my freshly valeted car for the drive home happy as larry at not paying a penny!
The level of customer service is amazing, I walk in to the dealership to ask about anything/get any work done, and straight away they're polite and treat me seriously despite going in there as a 23 year old in shorts and a t shirt with a mate in tow. They're strategy has clearly worked, as now I'm finding it hard to justify leaving the brand for whatever I buy next.