There are a few things to think about.
Coaxial cable will likely not have a positive impact on your RFI.
Unfortunately, urban locations are loaded with RFI. Antenna direction and distance are the primary ways of reducing the received noise. On a small lot, this is not always possible but improvements should at least be evaluated. For example, an electrically shortened antenna may allow the antenna to be located further away from local noise sources and oriented such that its directionality attenuates these noises.
Don't overlook the opportunity to identify and potentially eliminate noise sources. Start with your own house by powering your radio off of a battery and shutting down the house power and other battery powered devices within the house. If the noise level drops, start turning on individual breakers to help identify the sources of your local noise. Go RFI hunting in the neighborhood to identify other noise sources that might be correctable.
If the antenna is not well balanced due to factors such as uneven heights or trees or buildings near the antenna then the feedline can become unbalanced and be a point of ingress for noise. A 1:1 balun at the feedpoint may help mitigate the noise ingress.
Connecting a balanced feedline to an unbalanced tuner can also couple local RFI into the antenna system. The antenna side of an unbalanced tuner should have a 1:1 balun between it and the balanced line. A belts and suspenders approach is to also put a 1:1 balun on the coaxial side of the tuner going to the transceiver.