i have a 1991 corolla with about 140,000 miles on it.

a few months ago a noise started happening and i figured it was just a
plastic piece or something loose underneath the car, but now it's
getting worse.

the sound i hear is like a popping noise, or maybe like a piece of hard
plastic or rubber grinding/popping against the floorpan of my car.
sometimes it's just a tap or two when im driving, sometimes (like when
i put on the brakes) it's one tap or maybe two, and then (when i take
my foot off the brakes) more of a rapid rubbing tap-tap-tap - tap. but
it doesnt only happen when i use the brakes, it happens during normal
driving. it sounds like it could be something actually hitting against
the underside of my car while driving because i can feel the tap
through the floor of the car in the area right beneath the brake pedal.

it does NOT only happen when i turn, and it is noticable at all speeds
but seems random (doesnt increase with speed). at first i thought it
was related to the strut on the front driver's side (just had the back
two replaced - the noise was happening before and after this, and the
back ones were only replaced because one rusted totally out).

i want to take it somewhere and have it checked but i just moved to a
new town and dont want to have some mechanic take advantage of the
situation and try to replace every thing on the car. i wouldnt know
what to even wiggle or feel for underneath the car and it's kind of
hard to get under there (limited space to work with).

i dont know if it could be the sway bar or some sort of other linkage
totally lose and flopping around and hitting the floorpan, or if
something else could be very loose like that, or what i should look
for. if anyone has a picture of the underside of a 91 corolla that
would be really helpful, as would any advice on what to try.

thanks.