DM's walk in shower drain is sometimes blocking and overflowing - strangely enough, not all the time. Definitely no hair buildup - she's elderly and gets her hair done at a salon weekly. There's no smell or foul buildup of soap.
We've tried the usual drain cleaner stuff, foam, bicarb etc and nothing helps. I've checked the outside outlet and it looks clear - no leaves etc.
The drain makes a physical noise now and again, like a gentle knocking. Any ideas?
My DM is reluctant to pay call out fees until we very much have exhausted all possibility of us sorting us themselves. Help!