I've had the KRK RP5 G3s in my home studio for a couple of years, and overall, they're pretty solid for their price point. In terms of clarity, they perform quite well with clear mids and highs, which is great for detailed mixing tasks. However, when it comes to the low-end response, they can be a bit lacking. This isn't uncommon for monitors of this size (5-inch woofers), so if your work heavily depends on accurate bass reproduction, you might want to consider pairing them with a subwoofer.
Regarding hissing or noise issues, some users have reported slight hiss at high gain settings, but my pair has been relatively quiet. Just ensure your audio interface or any other gear connected to the monitors is of good quality to avoid introducing noise through the signal chain.
For positioning, it's crucial to place them at ear level and make sure they are angled towards you forming an equilateral triangle with your listening position. Also, keeping them away from walls can aid reduce unwanted bass reflections. If possible, use isolation pads or stands which can further improve sound clarity by minimizing vibrations transferred through your desk or shelf.
Hope this helps with your decision!