It may be helpful if you gave the model number of the device that you are speaking of, If your radio has a Bluetooth or 3.5 headphone jack go with that because the FM Receivers have a bad habit of giving poor quality but there is several work around..,
1. If you have a2dp Bluetooth on radio just stream with Bluetooth,
2. If you have a 3.5 input jack you can do like me and use a Bluetooth receiver that Verizon carries that receives Bluetooth signal and transmit out a 3.5 jack which is a clearer option.
3. But if you only have a RF option, you should be able to pick up transmitter from Verizon, Walmart,K-Mart, Best Buy or any electronic store. I bought one from Verizon and I was impressed with sound quality.... It sounded fine sitting parked but when you drive the reception fluctuated just like the radio signal does which wasn't a good thing.
Try a Jabra Clipper Bluetooth Stereo Headset or a Jabra Cruiser In-Car Bluetooth Speakerphone
Verizon appears to pull these devices but I am sure you can find them still on sale in some stores and online.