Yesterday I noticed a few rather loud "ding" sounds coming from somewhere under the car. "swaybar / suspension??" Today there was a loud metallic grinding noise which happened twice but for only one second intervals. What could there be wrong?

ps. my winter rims are quite close to the front calipers (6mm clearance approx) but I've driven on them for over 1000 kms and this is the first time I've heard this noise.

Weather is about - 20c. Could the cold be a problem?

Any input would be great!!
Thanks