Tapping on a regulator or any part with a screwdriver to me automatically indicates problems. I would think that you probably have an iffy regulator and it may need to be replaced. Also, check all the grounds. It may be a simple a fix as that. Make sure all grounds are clean and bright.
I don't have anything on the 154 as in a IH Service Manual but I do have a bit on the I&T IH-Series Shop Manuals
- IH-38 1974 Edition Complete
As was mentioned in a previous thread, you could check the regulator itself - basically for corrosion or the points actually opening and closing, but adjusting may make other problems appear. Check the grounds first then if that doesn't help, you could take the regulator to an Authorized AC Delco Service Centre. They could check it and if it is bad then you could get a good quality OEM replacement (or a warranted replacement that they offer. Mine was an RCP13227 - Generator and Cut-Out