My plastic clips are new but when I raise or lower window, roughly where the glass is 1/4 up to about 1/2 up, I hear some grinding noise.

Does this mean the plastic pulleys are going out? If truly plastic pulleys, then my only option is a new window regulator, which is about $150 at local dealer.

For those with "sliding clips" issue: what are the symptoms?

nuts. I started hearing my right front window making clicking noises as itgot to the last 2-4 inches to close. then i hear it rattle a bt as its fully closed.
Time for the Win Reg clips and perhaps these slider clips (have to research what they are for actually).
thanks for the DIY CN90

Mike I would do them both - if you only do the black window clips you potentially leave a weak point in place (the slider clip is known weak)

Jay I will def be doing both black window clips and aftermarket white regulator slider clips (these clips I just ordered).
for the rear windows I noticed there is two options for the window clips tho...
parts 51357011680 or 51338254781 (for double glazed windows, also the same part number as for the front windows).

Hmmm which part number is newer? They are probably cheap enough you can buy one of each for the years lol

its not an issue of which is newer, but of design as they are different.
the white tabs ending in 1680 are $7USD (works out to be about $11 CAD at todays exchange) as opposed to the $1 black clip (ending in 4781).
Calgary BMW is selling those white clips (part ending in 1680) at $18 CAD and the black clips (which are same as front windows, ending in part number 4781) for $4 CAD.
holy crap.
I wont be buying till I have the door pannels off I guess.

For my 2001 E53, those part numbers and colors are both correct, and the prices are about right. The ...1680 are for the rear windows, with one needed per window. The ... 4781 are for the front windows, with two needed per window. I think the ...4781 will fit in the rear, but they are slightly different size, and the 1680 is correct back there.

Regarding whether to try replacing the regulator clips (or "sliders") with the regulators in situ, I will advise that the effort to R+R the regulator once you have the panel off and the window disconnected, is relatively minor. And at least for the rear regulators, it took me a fair bit of wrestling and swearing to get the new regulator clips installed. Would have been FAR more difficult to try doing it with the regulators still installed.

so has anyone replaced the rear regulator slider clips and can give advise about how to remove the OE clips from the cable and how to install the cable ends into the new slider?
I have the new RegulatorFix brand clips to install but the way the wires connect to the rear slider clip is totally different than the fronts (which I replaced months ago).

I can't figure out how to get the cable ends out of slider as cable is sooooo tight.

I've done it (as mentioned above). Don't remember many details. The only notes I made for myself were that I did not use zip ties to strengthen it, like I did on the front regulator clips.

For the rears, I couldn't even get enough slack in the cable to disconnect the cable End knobs and springs that are sitting in the plastic sliders. And I worried if I DID get them out of the OE sliders, how do I get enough slack to fit them INTO the new sliders. I took off the motor to look for more slack, but nope, as that would have lead to a whole new can of worms.
So for the rear doors, I'm going to just buy the whole regulator (cables, sliders, arms) new as one piece on the day the old ones break. Its near impossible to replace that slider without having to find extra slack somehow. And new regulator from Dorman (cheap name yes) is only $70 CAD but it saves you time by not having to wrestle with clips. Its a MUCH faster R&R than buying just the clips and trying to find a way to remove the cable ends and re-install the cable ends into the sliders.