while driving my 87 se in like 3rd or 4th gear i believe when the car hits like 3700 rpms everything grows strangely quiet and ever so slightly hesitates until 4000 rpms when it grows loud again. it is very weird. the car is stock except for a air filter, although it did this before installing the filter.

 

Common problem...try searching for the fix.

 

At around 3800 the ECU is switching on the secondary injectors & cutting back half on the primaries.
This works smoothly only if your grounds are perfect.

It usually goes like this:
1) The primary ground (battery to starter) gets old.
2) some load picks up the firewall to bell housing ground (which is just a cheesy clip) & it gets weak.
3) Now the sensor & control grounds start seeing alternator & spark noise.
4) The ECU goes nuts.
5) You go nuts.

Clean up your grounds (bright shiny metal to metal contact).
Then maybe add a ground from the alternator frame to the spark coil mount.

Drive & smile!