Just did a minor adjustment to my bathroom vanity sink faucet. Both hot and cold water come out from a single handle fixture. Turned both hot and cold water off under sink before repair. Now, when I turn the cold water on I hear a very loud BANGING and VIBRATING. This occurs only when the cold water is turned on full force. It is not happening with the hot water. I think it's because I have air in the line now. (But who knows, I'm not much when it comes to DIY plumbing). I am proud that I fixed the leaking, dripping faucet, but this problem is WORSE!!! Please help, would be most appreciative. I will add, I opened all the other faucets in the house thinking this would help, it didn't. THANKS

I'd say that the washer in the supply stop under the sink came loose when you turned the water off and back on. You might try turning that valve off and back on again, sometimes that will put the washer will get put back into position. If that doesn't work you'll either need to replace the valve or disassemble it and see if it can be repaired.

One thing you can be sure of is that it is NOT "air". Any air would have been expelled as soon as you turned the faucet on.

Same thing happened to my toilet shut-off, a Brasscraft. Washer came unseated from the stem after shutting it off and then reopening, and had stuck to the seat. It let only a low flow of water through, with a loud vibration. A rebuild fixed it. Brasscraft sells rebuild kits for them.