I agree the 396xt has very good receive.but this 436 I just got is pretty close to the 396xt..my original 436hp there's a big difference. The 396xt blows that one away.
I wonder if it has anything to do with the battery door interference issue that has been a very active thread.
Try them both with an external antenna if possible.
I tried shielding my battery door in my 436 but if made zero difference when using the stock antenna. Many reported the same results so it seems that some 436 models do not emit interference from the battery compartment while some do.
That problem is non existent when using an external antenna so the theory is that the factory antenna is picking up internally generated noise from the radio itself.
Many claim shielding the battery door made a huge improvement mostly in the 450 MHz area.
I actually have two 436 models and do not get any RFI from the radios when using a duck antenna.
How far apart are the serial numbers from your original 436 compared to the eBay model?
There could have been an RF board change in between your models.
Using an external antenna should prove if the poor reception model is picking up internally generated noise.
The only other easy thing you may try if you have not already is swapping the SD cards between the models and see if the poor performance follows the card to the other radio.
That would point to a noisy card.
Any external antenna should work if you can place the antenna 10 or more feet from the radio as those with internal noise appear to report the noise is very low level so moving the antenna away from the radio is enough to improve reception back to normal.
If the poor reception model has any of the issues Uniden is fixing for free, taking advantage of that offer may just fix you up.
You could also make an antenna if you have a 6 foot or longer hunk of coax laying around with a BNC connector on one end. Just strip off about 6 inches of the shield on one end and find a weak UHF signal and see if the reception equals out between the two radios. If it does equal out the reception, then you may be a victim of the internal noise many are finding.
My two 436 models are old and new. One was purchased when they first released them and the other is fairly new with a recent serial number range but neither show any signs of internal noise. I even sniffed them both with an analyzer but neither were emitting anything bad so doing the battery door shield mod did nothing of course. I even played with different SD cards including the factory cards but could not get either to produce the noise that the large thread is talking about.