Funny noises after high speed run

Had to dash up the motorway last night so was in a bit of a hurry, car was behaving itself perfectly, cruising with the traffic at 90+ for about 30 miles but then onto a deserted dual carriageway at 120+ for about 3 miles. I slowed to about 70 before braking gently down to 40 ish then again before the roundabout at the end.

This is when I got a bizarre noise, sounded like a creaking at regular intervals about 4 times per second each time I braked or went over a bump, seemed to be coming from somewhere under the bonnet, just the otherside of the bulkhead to my right foot.

I drove slowly off-boost for about 10 mins and let the car idle for ages when I stopped and the noise seemed to go away. This morning it hasn't come back.

Just wondered what it was really?

Other than the noise I was very impressed with the Octy's motorway cruising, first time its been over 70 and it was so much nicer than my old Astra LOL!

Speeds given in kmph... honest officer