When I turn the water on to take a shower it leaks underneath to my basement ceiling. But when I run the water to take a bath it doesn't leak. It only leaks when I take a shower, could this be a bad diverter valve or lose shower head fitting, I have opened up the ceiling in my basement to see if I can find the leak but I can't really see where it is coming from. Should I make a hole in the wall hext to the shower head to see if I can see the leak? Should I call a plumber? Thank you

Before making any holes, check that the shower head is not leaking where it is connected to the pipe sticking out of the wall. If it is loose, you could have a small amount of water spraying back to the wall causing the leak downstairs. If it is leaking, a little teflon and a pipe wrench will do the trick.

Also, since this appears to be a tub/shower combo, there might be an access port on the wall behind the tub spout that could give you the visibility you need to find the leak. Finally, the decorative plate behind the water knob is probably only held on by 2 screws - you may be able to remove it and see what is happening in there.

The chances are strong that this is a leaking diverter or the shower arm like dmrlook suspects. Befire starting any repair turn the shower on and catch all of the water in a big bucket with no spray of splash on the walls. If there is no leak then you may have some bad grout of caulking in the enclosure. If there is a leak remove the handle and the esctcheon plate to inspect the mixng valve. Let us know if the valve is wet or if the pipe going up from the valve is wet.