Use different speaker cables to test the system again. Many times a speaker issue may actually be a faulty cable issue. Replace the audio cables in the TR225 with a new cables and play audio through the system. If things sound fine then you know it was just a bad cable connection. Throw away the faulty cable or cables.
Check your electronic signal chain. Many audio speakers connect to power amplifiers, media players, televisions, and sound mixers. An electrical problem in any of these devices can cause a buzzing or humming sound in the speaker. Remove all electrical components from the JBL speaker. Choose one electrical device like a DVD player and connect it to the TR 225. Play an audio track and examine the results. Repeat this step with every electrical device in your signal chain until you've found the problem unit.
Reverse the speaker polarity to boost low-frequency output. If the speaker's low-end sounds muddy or cluttered, it could be out-of-polarity with the other JBL speaker in the system. Press the small black button above the audio input jacks to reverse the polarity.
Remove the speaker's protective covering. Every JBL speaker has grill in front of to prevent any direct damage. Remove the screw holding the speaker grill with a 1/4-inch screwdriver. Slowly pull the grill away from the speaker cone. A small rip in the cone can cause sound damage. A rip may also mean the speaker needs to be replaced.
Remove the speaker cone from the casing. Remove the screws around the speaker cone with a 1/4 inch screwdriver and place them off to the side. Pull out the cone and examine all wiring inside the casing. Look for any signs of wear in the wires. There may be a wire connection that needs re-soldering. Clean off the speaker cone with a soft wash cloth and water. Dab the wash cloth in a bowl of water and wring it out before touching the speaker cone.