Lots of taps on the Squid, so, let's assume that by experimenting you have found the best match to your horizontal loop. (The idea here is that when impedances are matched there will be maximum transfer of signal).
From the Squid, run a good quality coax to your RX location. "Good" means not only low loss but also well shielded. Some coax has very minimal outer braid shielding.
Your noise could be from nearby radio transmitters or locally generated electrical/electronic QRM or both. If you have noise pickup problems, consider using a common mode filter (choke) as close to the RSP2 RX as possible. Lots of info on the internet on how to build a common mode filter or you can purchase one already built.
Leave the ferrite on the USB cable or get a better quality (shielding again) USB cable. This cable can pickup lots of noise and transfer it to the RX.
Looked at the specs for your RSP2 and like my RSP1 it has a 12 MHz low pass filter. So, especially below 12 MHz you need some help. Have found here that an antenna tuner at the RX input helps considerably in peaking the desired signal. Pulling it out of the noise so to speak. Even something as simple as an MFJ 956 works wonders.
Don't know where on the outskirts of GR your QTH is located, but if it is near any of the half dozen or so AM broadcast stations in your area, you may have to build a notch filter(s) (also known as a wave trap) specific to the frequency of the offending station(s).
If the antenna is bare stranded wire, in time the wire will oxidize between the strands and create high resistance and a noisy situation. Copper oxide is a good rectifier... think mixing products.
Use bare or insulated solid wire or insulated stranded wire.
Just a few thoughts that hopefully may be of some help.