Check the gap on the ramp bonus switch. If it's too close, vibration will set it off. If you're not sure stick a business card between the contacts and see if the problem goes away.

Ditto on the tilt switch adjustment.

If OK, then we'll look at more complicated things.

If you look at the contacts you'll see two metal arms that are pushed together when the switch is closed. See the pictures in the following article.

http://pinballrehab.com/1-articles/solid-state-repair/routine-maintenance/150-cleaning-gold-plated-contacts

When the switch is not closed it should have a gap of about .020" to .032". Very roughly a business card thickness (or buy some feeler gauges and be exact, but not really necessary).

Unfortunately this is not an exact science since most contacts have been bent to hell and back (meaning they may be more flexible than they should be, and will vibrate more than they should). As I said put a business card between the contacts and see if the problem goes away. Then go from there.