Sounds like you've either washed some grit into your chain, or possibly have a spot of rust. It's a common problem when folks wash chains but don't do a thorough job.

Before doing anything else check for stiff chain sections by holding some tension off the RD idler so the lower loop sags a bit & back pedaling slowly. Look of any links that don't straighten out immediately as they come off the lower RD pulley. If you have any stiff links that accounts for the clicking, ut the next step is the same regardless. You need to do a more thorough job washing the chain to get all the grit out.

If you can remove the chain using a re-usable master link so much the better. Take it off and put it into a plastic Coke (or pepsi or whatever) bottle, fill 3/4 with hot tap water and your favorite dish detergent. Shake like crazy, then let the dirt settle a bit and pour it off. Repeat until the liquid stays perfectly clean, then rinse with fresh water plus 1 tiny drop of detergent to manage PH. Shake out the chain & dry it in your oven at 200 for 10 minutes to ensure that it's perfectly dry before re-lubing with your favorite lube. (hopefully my stuff)

If you can't remove the chain it's basically the same using a chain cleaner gadget, but it's slower and messier, and you'll need a hair dryer (heat until the chain feels warm) or a final rinse in fuel grade alcohol (methanol, not isopropyl) to ensure that it's dry. Re-lube immediately after.