As an experiment, run a shot, without coffee in your espresso machine into a clean cup. Smell it. Taste it. Smell or taste anything? You shouldn’t. Clean your machine so your espresso will have a pure, clean, unadulterated flavor.
Take your shower screen off as well as any other pieces that come apart in this area, and scrub it clean and maybe use some citric acid or vinegar to get all those old coffee oils off. Rinse, dry and reassemble.
Descale your water tank using any commercially available coffee pot cleaners or you can use citric acid.
Run lots of clean fresh water through your machine. Now repeat the shot of water with no coffee. Smell. Taste. Now isn’t that better?