If you don't already have some, check out Harbor Freight and buy a set of vehicle trim tools, then pry open the grill. If you hear cracking/popping it could be as simple as the paper cone separating to the voice coil starting to rub against the magnet. Likely best fix is to replace the speaker. With what is up to you.
I changed speakers in an ES350 with standard radio and while the new replacements had better and clearer highs, the mids and lows were no improvement if not worse than OEM. Choose carefully. Also I believe you may not have a good chance at matching the speaker impedance.