I can't find where it explicit comes from but it always sounded like MB
Below are the specs for MB and chassis - so I have to figure audio beep is on MB
ANTEC 200 specs 
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CPU cut-out allows for easy installation of CPU coolers
Bottom-mounted power supply isolates heat and noise
Perforated front bezel delivers maximum air intake
Cable management compartment organizes cables discreetly
Front-loaded HDD cage for up to 6 hard disk drives
Cable management ties help keep your case tidier
10 drive bays:
- 6 x internal 3.5" HDDs
- 3 x external 5.25" HDDs
- 1 x external front-loaded hot swap 3.5" SATA hard drive caddy
7 expansion slots for plenty of flexibility
Cooling system:
- 1 x top special 140mm TwoCool™ fan
- 1 x rear 120mm TwoCool™ fan
- 2 x front 120mm fans for HDDs (optional)
- 1 x side 120mm fan for graphics cards (optional)
Front ports:
- 2 x USB 2.0
- Audio (AC'97 and HDA compatible) In and Out
Washable air filters for quick, easy cleaning
Maximum video card size: 11.5"/292mm (Note: some video cards may require removal of the adjacent hard drive cage)
Motherboards: Mini-ITX, microATX, Standard ATX
Power supply not included
Unit dimensions:
- 17.7" (H) x 7.9" (W) x 18.5" (D)
- 450mm (H) x 200mm (W) x 470mm (D)
Box dimensions:
- 21.3" (H) x 20.6" (W) x 11.2" (D)
- 541mm (H) x 523mm (W) x 284mm (D)
Net weight:
- 13.9 lbs / 6.3 kg
Gross weight:
- 16.8 lbs / 7.6 kg
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Gigabyte GA-EP45-UD3R spec
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General
    Product Type Motherboard - ATX
    Cache Memory None
    Chipset Type Intel P45 Express / Intel ICH10R
    Max Bus Speed 1600.0 MHz
    Processor Socket LGA775 Socket
    Max Processors Qty 1.0
    Compatible Processors Pentium Dual Core,
    Celeron 400 sequence,
    Celeron Dual Core,
    Core 2 Duo,
    Core 2 Quad,
    Core 2 Extreme
Memory
    Max Supported Memory 16.0 GB
    Supported RAM Technology DDR2 SDRAM
    Supported RAM Speed 667 MHz,
    800 MHz,
    1066 MHz
    RAM Features Dual channel memory architecture
Audio
    Type High Definition Audio (8-channel)
    Audio Codec Realtek ALC889A
    Compliant Standards High Definition Audio
LAN
    Network Controller Realtek RTL8111C
    Network Interfaces Gigabit Ethernet
    Modem None
Expansion / Connectivity
    Expansion Slot(s) 1.0 x Memory ( 1.8 V ) - DIMM 240-pin,
    3.0 x PCI Express x1 - LGA775 Socket,
    3.0 x PCI Express 2.0 x16,
    1.0 x PCI,
    4.0 x Processor
    Storage Interfaces Intel ICH10R : ATA-133 - connector(s): 2 x 7pin Serial ATA - 6.0 device(s) - RAID 0 / RAID 1 / RAID 10 / RAID 5,
    Serial ATA-300 - connector(s): 1 x 40pin IDC - 2.0 device(s) - RAID 0 / RAID 1 / JBOD,
    Serial ATA-300 - connector(s): 6 x 7pin Serial ATA - 2.0 device(s)
    Interfaces 1.0 x IEEE 1394 (FireWire) - Line-out (center/subwoofer) - Mini-phone 3.5 mm,
    1.0 x Audio - Generic - TOSLINK,
    1.0 x IEEE 1394 (FireWire) - Line-out (side surround) - Mini-phone 3.5 mm,
    1.0 x Network - SPDIF output - Mini-phone 3.5 mm,
    1.0 x Keyboard / mouse - Generic - Mini-phone 3.5 mm,
    1.0 x Hi-Speed USB - Floppy interface - RCA,
    1.0 x Audio - Ethernet 10Base-T/100Base-TX/1000Base-T - 34 pin IDC,
    1.0 x Audio - Line-out - 4 pin USB Type A,
    1.0 x Audio - SPDIF output - 4 pin FireWire,
    8.0 x Audio - Line-in - 6 pin mini-DIN (PS/2 style),
    1.0 x Microphone - Line-in - Mini-phone 3.5 mm,
    1.0 x Audio - Input - 4 pin MPC,
    1.0 x Audio - Line-out (rear) - 6 pin mini-DIN (PS/2 style),
    1.0 x Mouse - Mini-phone stereo 3.5 mm,
    1.0 x Storage - RJ-45,
    1.0 x Audio - 6 pin FireWire
    Additional Connectors (Optional) 4 x Hi-Speed USB,
    1 x IEEE 1394 (FireWire)
    Power Connectors 8-pin ATX12V connector,
    24-pin main power connector
Features
    BIOS Type Award
    BIOS Features DMI 2.0 support,
    ACPI 1.0b support,
    SMBIOS 2.4 support
    Hardware Monitoring Chassis fan tachometer,
    Chassis temperature,
    CPU core temperature,
    CPU overheating protection,
    System voltage,
    Power supply fan tachometer,
    CPU fan tachometer
    Hardware Features Q-Flash,
    Time Repair,
    Ultra Durable 3,
    Chassis intrusion detection,
    GIGABYTE Dynamic Energy Saver Advanced,
    DualBIOS,
    EasyTune6
Miscellaneous
    Cables Included 1.0 x Serial ATA cable,
    1.0 x IDE cable,
    1.0 x Serial ATA internal to external cable,
    4.0 x Floppy cable
    Software Included Norton Internet Security,
    EasyTune 6,
    Drivers & utilities,
    @BIOS,
    Q-Share
    Width 12.0 in
    Depth 9.6 in
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