Well...
Since I've been refurbishing Fantom vacuum cleaners for a very long time, it's with my professional opinion to opt out on buying this Thunder. I've had many cases like this where people bring me their Thunder complaining about a "loud motor noise". There are two main factors for this issue, 1. an object is stuck in the brushroll causing a loud noise to be made, or 2. the motor is dying and needs re-coiled and lubed.
If you want to buy this machine, I will wish you luck. Even if it may not work, with a little bit of elbow grease, those can become very nice Thunder parts. And to add, the Thunder was one of the more popular Fantom models. So finding a new Thunder will not be difficult. I come across Thunders all the time.