One of the most common indications of wheel seal failure is when your vehicle starts to leak fluid. This can be easily spotted if you park your car in the same spot for a few days and notice a puddle of fluid beneath it. Another indication is when you hear a hissing noise coming from the wheel area while driving. This is caused by air escaping from the wheel due to a failed seal. If you suspect that your wheel seal may be failing, it's important to have it checked out by a mechanic as soon as possible.