A clicking noise coming from a hard drive is a sign of a mechanical failure, which can cause data loss or corruption. Replacing the bad drive as soon as possible is the best way to prevent further damage and restore the RAID array to a healthy state. Reinstalling the drive, resetting the RAID software, or running a chkdek on the drive will not fix the underlying hardware problem and may even worsen the situation.

The 2.4 GHz standard is better at propagating through solid surfaces, giving it the longest signal range. However, the 2.4 GHz band does not support a high number of individual channels and is often congested, with both other Wi-Fi networks and other types of wireless technology, such as Bluetooth. Also, microwave ovens work at frequencies in the 2.4 GHz band. Consequently, with the 2.4 GHz band, there is increased risk of interference, and the maximum achievable data rates are typically lower than with 5 GHz.
The 5 GHz standard is less effective at penetrating solid surfaces and so does not support the maximum ranges achieved with 2.4 GHz standards, but the band supports more individual channels and suffers less from congestion and interference, meaning it supports higher data rates at shorter ranges.

The technician should check the MAC filtering list next as the new router may have a different MAC address than the old router. Reference: CompTIA A+ Certification Exam Guide, Exam 220-1001, Page 332

SAS stands for Serial Attached SCSI, which is a bit serial interface successor to SCSI sponsored by ANSI and introduced in 20041. SAS is the most common interface for enterprise HDDs, especially those with high performance and high reliability requirements, such as 15,000rpm drives23. SAS offers faster data transfer speeds, lower power consumption, and better scalability than other interfaces1.